For landing on heavenly bodies such as a planet or the moon, landing spacecraft (e.g. a so-called lander or landing module) are conventionally equipped with landing gear including plural landing legs and a respective landing foot pad mounted on the free distal end of each landing leg. For example, three landing legs may each have a respective landing foot pad either rigidly or pivotally mounted on the free distal end of the respective landing leg. For reducing the shock loads that arise during touchdown and landing of the spacecraft, and particularly when the foot pads of the landing feet contact and settle onto the landing ground surface of the heavenly body, the landing legs of the spacecraft can be equipped with shock absorbers, or also with so-called crush elements or crumple zones made of aluminum honeycomb, for example. Also, in order to prevent the foot pads from sinking too deeply into the landing ground surface of the heavenly body, which is often very soft or loose ground, the foot pads are designed with a sufficiently large surface area so as to distribute the landing contact forces over this enlarged surface area of the foot pads. Moreover, while a rigid connection of the foot pads to the distal ends of the landing legs may be mechanically simpler, a pivotal connection of each foot pad onto the respective landing leg allows each foot pad to adapt its position better to the respective local contour of the landing ground surface at the location at which the respective foot pad touches down. For example, the US Apollo Lunar Module included a landing gear of the abovementioned general type with a pivotal mounting or connection of the landing feet on the landing legs.
Furthermore, because the pivotally mounted landing foot can adapt to the contour of the landing ground surface without hindrance in this manner, it also helps to prevent the application of excessive bending moments onto the landing legs and especially the shock absorbers thereof. Namely, a rigidly mounted landing foot would tend to exert a bending moment on the landing leg when the landing foot is urged to adapt its orientation to the contour of the landing ground surface during the touchdown and landing process. That is avoided by the pivotal connection of each landing foot on the respective landing leg. However, in this case, the pivotal connection must be locked or blocked to prevent pivoting during the launch and flight of the spacecraft, e.g. on its transport rocket, and also during the extension or deployment of the landing gear until a time shortly before the landing of the spacecraft on the heavenly body, in order to prevent the foot pads from having an uncontrolled or random starting position at the beginning of the landing process. Such locking or blocking of the pivotal connection between the landing foot (e.g. particularly the foot pad) and the landing leg can be achieved by an additional mechanical connection that is designed to withstand the loads arising during the launch from earth, during the spaceflight, and during the approaching flight to the target destination landing site on a heavenly body, without disruption of or damage to the mechanical connection. Furthermore, however, the mechanical connection must be designed so that it will be overcome or disrupted or broken as a result of the higher forces that will necessarily arise at the moment when the foot pad touches down and contacts on the landing ground surface of the heavenly body.
U.S. Pat. No. 6,227,494 (Turner) discloses a landing gear arrangement for spacecraft, comprising landing legs and landing feet with foot pads pivotally or articulately connected to the distal free ends of the landing legs oriented away from the spacecraft body. Furthermore, in the disclosed arrangement, mechanical connections are additionally provided only for the structure. The landing leg may include a honeycomb crushable portion for absorbing landing forces, and a sensor assembly may be provided within the spherical bearing assembly of the pivotal connection joint for providing a touch-down signal. The sensor assembly has a complicated construction with many components to be incorporated in the connection joint assembly. There is no redundancy and no interaction or cooperation between a mechanical triggering and an electrical triggering at the time of ground contact, and there is also no provision for thereby releasing a fixing or blocking of the foot pad.
When a spacecraft is to land on a heavenly body having only a thin atmosphere or no atmosphere, such as the earth's moon for example, it is further known to reduce or minimize the forces that arise during the landing by slowing-down or braking the motion of the spacecraft until shortly before its touchdown on the landing ground surface. Such a braking process is usually carried out by appropriate firing of separate braking engines, e.g. so-called retrorockets or retrothrusters. Sensors are provided to control the firing of the retrorockets or retrothrusters based on the distance from the landing ground surface. For example the spacecraft may be equipped with an electromechanical surface sensor or with a contactless distance measuring sensor, for example using a radar system, to generate a signal that causes the retrorockets to be switched off, so that the spacecraft completes its landing and settles down onto the landing ground surface. The terms braking engine, retrorocket and retrothruster are each used generally and exchangeably herein, to cover both rockets and thrusters and all other means of producing a braking thrust for slowing, reversing or maneuvering the motion of a spacecraft.